1. Field of the Invention
The present invention relates to a vehicular power converter which is mounted in a vehicle or the like and, more particularly, to a heat radiation structure of a power converter having a power circuit section and a control circuit section.
2. Description of the Related Art
A power converter generally includes a power circuit section having a converter constituted by switching elements for converting a direct current to an alternating current of any frequency and a smoothing capacitor etc., and a control circuit section having a function for outputting a signal for controlling the switching elements and a function for electrical protection of the device. These sections are accommodated in a case. A power converter for regulating the input power of a three-phase motor incorporates two pairs of switching elements for each phase.
Since a power circuit section is used for regulating the input power to a motor, the electrical power rating is generally large and heat generation in the switching elements or the like is also large. Therefore, a converter is mounted on a base provided on one surface of a case, and cooling fins are provided on the surface outside the base to radiate the heat generation in the switching elements and to prevent an excessive temperature rise.
On the other hand, a control circuit section is formed by integrating a drive circuit and power supply circuit for driving the switching elements and a control circuit section including a microcomputer and a large capacity memory, which are formed on both surfaces of the substrate; and the control circuit section also has heat generation like the power circuit section.
As a known technology adopting countermeasures against heat generation of such a power circuit section and control circuit section, there is a power converter disclosed in Japanese Unexamined Patent Application Publication No. 11-69774, for example. In this technology, a power converter, a smoothing capacitor, and the like are mounted on a cooling fin base having cooling fins; a high-current substrate equipped with electronic components on the upper part thereof is provided; a control circuit substrate is further provided on the upper part; and a cover for covering all of these is provided, wherein the cover is provided with independent ventilating holes to draw cooling air for the control circuit, and the cooling fins and control circuit are simultaneously cooled with a predetermined amount of air by cooling fans provided outside the device.
In the above-mentioned known technology, some cost for mounting cooling fans on the case and consideration for the life-time of the fan are required and, more particularly, when this technology is applied to a power converter for use in a much more harsh environment, for example, in the case of a vehicular power converter, the reliability has been limited.
Further, there has been a problem in that provision of ventilating holes in the case cannot be applied for the above-mentioned vehicle-mounted application and apparatus for use in such an environment necessary for waterproof protection.
Furthermore, in the known technologies, a control circuit section is cooled by circulating ambient air inside the case; however, there has been a case in which, since the heat generated in the power circuit section of the power converter is generally larger than that in the control circuit section, the heat generated in the power circuit section is transmitted to the control circuit section instead of being transmitted to cooling fins, and consequently the temperature of the control circuit section is increased due to this heat. Therefore, there is a problem in that cooling means for cooling the control circuit section is required to provide a heat radiation performance that can handle a heat generation which is larger than the heat generation of the control circuit section, resulting in increased costs.